The present invention relates to an optimization method of an aperture type of a projection aligner.
According to JP-A-7-37769 (particularly, pages 4 to 7, FIG. 2, FIG. 3), in order to simulate a projection optical image whereby a three dimensional vector component of an imaging distribution in a projection optical system with a large aperture can be calculated by a simple method, by dividing a mask and a pupil surface in a lattice, and tracing a light ray generated on the mask surface and a light ray generated from an image of diffraction of a light source to be projected on the pupil surface as being interfaced with the divided three dimensional vector component, a sum of an electromagnetic field and a light intensity on the imaging surface is calculated.
In addition, according to JP-A-11-195592 (particularly, page 3, FIG. 1), in order to realize an aperture, an aligner, and a pattern formation for a modification illumination capable of being applied to various patterns as avoiding the troubles of having to exchange, metallic plates are superposed with each other to form a zonal center masked portion and margin masked portions are arranged at the opposite ends of the foregoing center masked portion. Turning first and second knobs leads to change of mutual interval between a width of the center masked portion and the margin masked portion. For this reason, a variable aperture having a slit width and measure of which are variable is provided between the center masked portion and the margin masked portion and one variable aperture can apply to various patterns.
By the way, according to a lithography step of a semiconductor process, in order to form a pattern that is more delicate than a theoretical resolution defined by a wave length of a light, an illumination method, so-called oblique light incident illumination, may be used.
In a lithography step of an LSI, it is often needed that a pattern having a large spatial frequency (a period of repetition is small) and a pattern having a mall spatial frequency (a period of repetition is large) are formed at the same time at a single exposure. In the lithography step, there are various causes of varying a size of the pattern, however, as a typical margin of the lithography step for ensuring accuracy of the size, a focus variance margin and an exposure amount variance margin of an aligner are mainly used.
However, a kind of the patterns to be optimized is specialized to a repetition pattern of a line and space (L/S) having the minimum size. In other words, in order to develop a resolution property of a pattern having the maxim spatial frequency capable of entering a projection lens, the aperture type is optimized.